I'm kind of in the same dilemma. I want eagle range but don't want to sell a kidney to be able to climb a drop bar bike up steep bay area fire roads.

I think I am going to try swapping an XT cage on a GRX 812 derailleur so that I can run a double and up to a 46t rear cog. You may be able to get away with a 11-40 shimano cassette with your current rear derailleur.

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I use sram's 11-36 cassette on my gravel bike.

 

Provided you use either an Ultegra RX or GRX 2x rear derailleur, an 11-40T cassette should be fine; I had 42x27 + 11-40 + RX RD in Europe last year and all gears worked. And no, you shouldn't need a Roadlink or similar abomination. The 5800GS & 6800GS RDs handle 36T fine, but 40T is really pushing it, while the newer R7000GS & R8000GS should be okay with 40T. None of this is officially okay by Shimano, but it works nonetheless. YMMV if there's something weird about your bike, and the chain needs to be long enough to tolerate big to big or else sh1t might happen.

 

A little off topic, but why can't Sram or Shimano offer more cassette options?
I'm sure cost and carrying more sku's is the real issue, but with the cross over between mountain and gravel, it would be nice to see 11 or 12 speed cassettes in 10-38, 10-42, 10-46 in addition to what they have now.....just thinking out loud.

 

Seems like that 30/34 combo will you give you low enough gearing for your climbs?

 

3T has some great information on this topic.

https://blog.3t.bike/2020/01/12405/gravel-bike-tech-gears-for-tough-climbs-part-1/

But 30/34 is probably easy enough for 95% of all climbs without being two 'spinny'

 

OP - it think you'll be surprised what you can climb with 30-34 gearing on your 105. I actually just got the same bike (Topstone) in sora build a couple of weeks ago. My MTB is 1x11 with 30 chainring and 46T cassette, and i had the same thought when i first got my topstone.

But so far, i can climb hills around here (in CT). My suggestion is to give it a try before spending money on changing out your 105.

 

On the road, carrying not much, sure. On steep dirt, with overnight gear, not so much unless you're very fit indeed. I suppose Rule #5 (HTFU) could be invoked, but a bigger cassette might make things a lot easier...

 

A wider range cassette is always good to have, especially when rocking 1x.

 

I have a Cannondale Topstone Al with the 105 group set on order.
The gearing is 30/46 chainring and 11/34 cassettes.
I'm a MTBer and this will be my first road/gravel bike.
I live in the SF bay area and we have a lot of long, steep road climbs that I will be doing on this bike. I have ridden a few of these loops on my Ibis Ripmo with a 30t chainring with a 12 speed Eagle cassette (10x50).

I'm wondering if there is a rear cassette that would work with my 105 system that has a larger gear than the 34, like a 40? Or is 34 the max?

Thanks:thumbsup:

I live in Marin and ride all the steep fire roads around here. I have settled on 50/34 with a wolftooth tanpan so I can run an xt 11 speed derailleur with an xt 11-40 cassette. It works well. With your lower front hearing I suspect you'll be just fine with what you've got. I would upgrade to an ultegra RX or grx derailleur for the clutch.

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I run a 1x system with a 40t chainring and a 11-40 cassette, works for most of my riding, but every once in a while I do feel under geared.
I used to run 2x and then a stick somehow got caught in my rear derailleur and practically torn it off. I went 1x using my Sram Force 22 shifters, but used a little known secret of using a Sram 10 spd GX clutch rear derailleur. Shifts perfect throughtout all the 11 rear cogs. The left shifter is going to be used for a dropper post someday.

 

Thanks for the responses guys! I did a road loop yesterday on my Ripmo ( still waiting for the Topstone) and I climbed one of the more popular longer climbs ~ 3 miles and 1300 ft and I used the 30x34 or higher gearing during the climb to see what the low Topstone gearing would be like on these climbs. It was fine. So I figure the 7ish lb. difference between bikes and the heavy enduro 2.5 tires on the Ripmo vs the 40mm tires on the Topstone will make up something like one more gear in the back? In other words making the Topstone that much easier to peddle with the weight difference and the lack of tire drag.
Sound about right to you guys?
I have no reference.

 

I'm not sure how much difference the weight will make, but the tire size change takes you from about 25.5 gear inches (with 30/34 gearing) on the Ripmo down to 24.1 on the Topstone (because the tire circumference is smaller). So that's a real gearing change. The weight and rolling resistance difference are just gravy..